HPCC-12591 Add new method WsWorkunits.WUGetStats

GetStatsOption:
  default or 0 -> return stats data in xml;
  1 -> download stats data as an xml file;
  2 -> download stats data as a ZIP xml file;
  3 -> download stats data as a GZIP xml file.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>